Upgrade to Firefox 21 in Ubuntu 13.04

Firefox 20 has all the goodies and it is already available for stable Ubuntu releases such as Ubuntu 12.10 and Ubuntu 12.04. But what about Ubuntu 13.04? Ubuntu "Raring Ringtail" is already on beta and the final release will happen in a few weeks time. And it is yet to receive Firefox 20 update. It will be coming anyways before the final release. But if you are like me and want the latest and greatest of Firefox right now, here's what you need to do.